Re: [HACKERS] Postgres Speed or lack thereof

Vadim Mikheev <vadim(at)krs(dot)ru> writes:
> Tom Lane wrote:
>> However, with a UPS and an OS that only crashes about once every
>> other year, I feel pretty secure using -F ...

> However, it's easy to crash Postgres itself and lose
> committed transactions -:(

Surely not? The docs say (and a quick look at the code confirms)
that -F suppresses calls to fsync(2). It does not suppress writes.
Thus, a commit will still write the data out to kernel disk buffers.
All that fsync does is force the kernel to execute immediate disk
writes for those buffers. If I don't fsync, and the backend crashes,
the modified file data is still in kernel disk buffers and the kernel
is still responsible for seeing that those dirty buffers get written
out eventually.

(Of course, errors inside Postgres might cause it to write bogus
data, but -F isn't going to help or hurt for that.)

Not using -F means that you don't trust your OS, your hardware,
and/or your power supply. It has nothing to do with whether you
trust Postgres.

regards, tom lane